*{margin:0;padding:0;box-sizing:border-box}body{margin:0;font-family:sans-serif;transition:background .3s ease,color .3s ease}.app-container{display:flex;min-height:100vh}.sidebar{width:200px;padding:20px;flex-shrink:0}.sidebar h2{margin-top:0}.sidebar ul{list-style:none;padding:0}.sidebar li{margin:15px 0}.sidebar a{text-decoration:none}.main-content{flex:1;display:flex;flex-direction:column}.navbar{padding:10px 20px;display:flex;justify-content:space-between;align-items:center}.content{padding:20px}body.light{background:#f4f4f4;color:#000}body.light .sidebar{background:#2c3e50;color:#fff}body.light .sidebar a{color:#fff}body.light .navbar{background:#fff;border-bottom:1px solid #ccc}body.dark{background:#1e1e1e;color:#f0f0f0}body.dark .sidebar{background:#111;color:#ddd}body.dark .sidebar a{color:#ddd}body.dark .navbar{background:#222;border-bottom:1px solid #444}